The European Commission has hit the "pause" button on Google's proposed $12.5bn (£7.8bn) takeover of mobile phone company Motorola Mobility, and asked for more feedback from rivals and users who would be affected by the deal.

Among key questions that it has already tried to tease out are whether Google would favour Motorola over other handware manufacturers which license Google's Android software for mobile phones and tablets. Google has repeatedly insisted that it would not.

Although Google worked closely with Motorola to produce two "reference" devices for the first versions of some Android software – for the Droid phone and Xoom tablet – it has also worked with others, including HTC and most recently Samsung, on others.

The EC had been due to complete its deliberations by 10 January, but Amelia Torres, spokeswoman for the commission's competition unit, announced that "The deadline is suspended because the (European) Commission needs from Google certain documents that are essential to its evaluation of the transaction."

She added that "once the commission has all the necessary information, it will re-start the clock and publish a new phase one deadline on the website."

Google, which announced the $12.5bn deal in August, is looking to boost its patent portfolio and compete better with rivals such as Apple, which is in a series of court battles with makers of Android products. Microsoft has also persuaded several Android mobile handset makers to pay it a royalty on each one made, on the basis that they infringe a number of Microsoft patents.

US antitrust regulators are also reviewing the deal, which Google began negotiating soon after it missed out on a raft of patents auctioned in July from the bankruptcy of Canadian communications company Nortel. Sanjay Jha, head of Motorola Mobility, persuaded Google to lift its original bid by 33%, financial filings showed.

A Google spokesperson said: "The European Commission has asked for more information, which is routine, while they review our Motorola Mobility acquisition. We're confident the commission will conclude that this acquisition is good for competition and we'll be working closely and cooperatively with them as they continue their review."

The EC is also investigating whether Google's dominance of search and search advertising in Europe is being implemented in a way which would lead it to formally object to the way that the search engine does business in the single market. If it is found guilty there could be fines or instructions to change methods of working.